Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers.
Many audio systems encode audio signals into pulse density modulation (PDM) signals. As an example, some audio systems utilize “1.5-bit” encoding in which, for each audio channel, datagrams of two bits are used to encode three quantization levels, with one two-bit code being an invalid code. As another example, some audio systems use 2-bit encoding in which, for each audio channel, datagrams of two bits are used to encode four quantization levels. Oftentimes, two or more audio channels of a signal are encoded in a single PDM data stream, with alternating datagrams representing each channel in the data stream (e.g., a two-bit datagram representing a left audio channel, followed by a two-bit datagram representing a right audio channel, followed by a two-bit datagram representing the left audio channel, followed by a two-bit datagram representing the right audio channel, and so on).
In many audio systems, audio data in PDM format may be communicated via a single electrical conduit (e.g., package pin, trace, wire, cable, etc.). Because a transmitter (e.g., a processor) of a PDM signal may be powered on asynchronously with a receiver (e.g., a Class-D amplifier) of the PDM signal, detection methods are needed to determine the boundaries of PDM datagrams (e.g., determining where within the data stream a most-significant bit of a datagram is located) as well as determining which audio channel each PDM datagram is associated. In addition, it may be desirable to determine a sampling edge across all possible data formats (e.g., number of bits per datagram, mono audio, stereo audio) that leads to a deterministic and substantially zero delay.